Electrochromic properties of WO3 as a single layer and in a full device: From the visible to the infrared

Most of the applications of electrochromic devices (ECDs) concern the visible whereas there is a significant need for ECDs active in the infrared (IR) region. After optimization, WO3 thin films show significant variation in emissivity, as high as 78% and 49% in the MW (3–5 μm) band and LW (8–12 μm) band, respectively. The incorporation of the EC WO3 layer in ECDs is discussed in terms (i) of device configuration (i.e. position of the active layer on top or bottom of the device), (ii) of the choice of materials including the transparent conductive layer, electrolyte, counter electrode, and (iii) of the thickness of each layer. Initial trends in optical modulation of the ECDs are deduced from simulation of the optical indexes (n and k). Experimental data based on half-cell assembly confirm the modulation in emissivity in the IR region for WO3/Ta2O5/NiO-based devices with however lower values than the predicted ones.